The present invention relates to load leveling for leveling the energy consumption of loads in energy management systems and, more particularly, to an arrangement in which the gap times are provided between the off times of the loads of such systems.
Modern automated building air conditioning control systems typically use data processing and communication techniques for the control of the various loads and for the reporting of information from the various sensors located throughout the building. Digital processing and communication techniques have been used increasingly to reduce the installation and maintenance costs of air conditioning systems within buildings. Such systems usually incorporate one or more computers for processing information derived from the sensors and for controlling the air conditioning loads accordingly. The computers in such systems are controlled by energy management routines which attempt to reduce the energy costs of running the building's air conditioning and heating plants.
One such energy management routine which is often employed in such systems is duty cycling. Duty cycling recognizes that certain loads within a building can periodically be turned off in an effort to reduce the overall energy consumption for those loads. An interval or period of time is established during which the duty cycle program will determine the amount of off time and the amount of on time for that load during the interval. For example, an interval may be of 15 minutes duration. Each load is then assigned an on time and an off time during that period. A given load may have a 71/2 minute on time and a 71/2 minute off time during the assumed 15 minute interval. Thus, during the 15 minute interval between 8 a.m. and 8:15 a.m., the load will be operated on for 71/2 minutes and off for 71/2 minutes. During the next 15 minute interval between 8:15 a.m. and 8:30 a.m., the load will again be operated on for 71/2 minutes and off for 71/2 minutes.
More sophisticated duty cycling programs will adjust the on and off times according to changing conditions. As an example, temperature is often used in order to adjust the on and off times. As the temperature within a space increases, the on and off times of the loads within that space may have to be adjusted depending upon whether the space is in winter or summer control, whether the load is a source of heat or cooling, and whether the deviation between the temperature within the space and the desired temperature is excessive.
Although other energy management programs, such as peak demand limit and load shedding, may be provided in such systems, the present invention is directed particularly to load cycling. It is desirable, during a load cycling routine, to spread the off times uniformly throughout the period to minimize the energy consumption at any given instant in time during the interval. Thus, it is not desirable to have all of the loads on at a given instant of time. Although load leveling has been done in the prior art, prior art load leveling systems have not attempted to spread the off times uniformly throughout the interval so that there is a uniform gap time between adjacent off times, nor have such systems deenergized the loads by deenergizing first the load having the largest off time KW value, then the load having the smallest off time KW value, then the load having the next largest off time KW value, then the load having the next smallest off time KW value, and so on.